The purpose of this project is to elucidate the interaction of biomaterials used for specific implants with the physiological environment and to explore specially prepared biomaterials and design features with respect to their suitability and performance in a variety of contexts. Polyurethanes are an important class of elastomers for use in catheters, heart assist pumps, electrode insulation and similar implant applications. Variations in the basic chemical structure of these polymers as well as physically induced stress can severely reduce their effectiveness for long-term use as a surgical device. Previous studies undertaken by this project have shown a relationship between the molecular chain structure in resisting hydrolytic forces. Recent evidence suggests that physical forces such as stress induced during fabrication can promote a form of stress corrosion. In vitro test data and SEM photomicrographs of surgical explants of various polyurethane classes show that premature failure is often the result of a combination of forces acting on the polymer at stress risers. A strong corrrelation, exists between these in vitro and in vivo observations over short and long term periods of study.